Correlation between critical current density and n-value in MgB2/Nb/Monel superconductor wires

Field and temperature dependences of critical current density (J(c)) and n-value were evaluated from un-doped and carbon doped MgB2 wires, supplied by the Hyper Tech Research, Inc. In order to explore the possibility of persistent current mode, the variation of n-values for the different MgB2 conductors was studied in more detail. It was observed that the n-value decreased gradually with an increasing magnetic field and operating temperature. From the power-law relationship between the J(c) and the n-value, n proportional to J(c)(m), we found that there was a strong relationship, m = 0.371, for both wires at 4.2 and 20 K. On the basis of our experiments, a larger J(c) led to a higher n-value, whether there was doping or not. (C) 2010 Elsevier B.V. All rights reserved.